The word "serial" in warez context means a unique number which identifies the license of the software as being valid. All retail software uses a serial number or key of some form, and the installation often requires the user to enter a valid serial number to proceed. A serial can also be referred to as a "CD Key". When you search for "ashampoo burning studio 2014 serial" for example, you may find the word "serial" amongst the results. This usually means your warez download includes a serial number.